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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < strong aria-hidd
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2022-08-24 10:48:15 +00:00
< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2022-08-04 06:59:33 +00:00
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< h2 id = "714-示例-基于标记的xml解码" > < a class = "header" href = "#714-示例-基于标记的xml解码" > 7.14. 示例: 基于标记的XML解码< / a > < / h2 >
< p > 第4.5章节展示了如何使用encoding/json包中的Marshal和Unmarshal函数来将JSON文档转换成Go语言的数据结构。encoding/xml包提供了一个相似的API。当我们想构造一个文档树的表示时使用encoding/xml包会很方便， ， ； － ， ， ， － < / p >
< p > 这里显示的是和这个API相关的部分： < / p >
< p > < u > < i > encoding/xml< / i > < / u > < / p >
< pre > < code class = "language-go" > package xml
type Name struct {
Local string // e.g., " Title" or " id"
}
type Attr struct { // e.g., name=" value"
Name Name
Value string
}
// A Token includes StartElement, EndElement, CharData,
// and Comment, plus a few esoteric types (not shown).
type Token interface{}
type StartElement struct { // e.g., < name>
Name Name
Attr []Attr
}
type EndElement struct { Name Name } // e.g., < /name>
type CharData []byte // e.g., < p> CharData< /p>
type Comment []byte // e.g., < !-- Comment -->
type Decoder struct{ /* ... */ }
func NewDecoder(io.Reader) *Decoder
func (*Decoder) Token() (Token, error) // returns next Token in sequence
< / code > < / pre >
< p > 这个没有方法的Token接口也是一个可识别联合的例子。传统的接口如io.Reader的目的是隐藏满足它的具体类型的细节， ： ， ， ， ， < / p >
< p > 下面的xmlselect程序获取和打印在一个XML文档树中确定的元素下找到的文本。使用上面的API， < / p >
< p > < u > < i > gopl.io/ch7/xmlselect< / i > < / u > < / p >
< pre > < code class = "language-go" > // Xmlselect prints the text of selected elements of an XML document.
package main
import (
" encoding/xml"
" fmt"
" io"
" os"
" strings"
)
func main() {
dec := xml.NewDecoder(os.Stdin)
var stack []string // stack of element names
for {
tok, err := dec.Token()
if err == io.EOF {
break
} else if err != nil {
fmt.Fprintf(os.Stderr, " xmlselect: %v\n" , err)
os.Exit(1)
}
switch tok := tok.(type) {
case xml.StartElement:
stack = append(stack, tok.Name.Local) // push
case xml.EndElement:
stack = stack[:len(stack)-1] // pop
case xml.CharData:
if containsAll(stack, os.Args[1:]) {
fmt.Printf(" %s: %s\n" , strings.Join(stack, " " ), tok)
}
}
}
}
// containsAll reports whether x contains the elements of y, in order.
func containsAll(x, y []string) bool {
for len(y) < = len(x) {
if len(y) == 0 {
return true
}
if x[0] == y[0] {
y = y[1:]
}
x = x[1:]
}
return false
}
< / code > < / pre >
< p > main函数中的循环每遇到一个StartElement时， ， ， ， ， ， < / p >
< p > 下面的命令打印出任意出现在两层div元素下的h2元素的文本。它的输入是XML的说明文档， < / p >
< pre > < code > $ go build gopl.io/ch1/fetch
$ ./fetch http://www.w3.org/TR/2006/REC-xml11-20060816 |
./xmlselect div div h2
html body div div h2: 1 Introduction
html body div div h2: 2 Documents
html body div div h2: 3 Logical Structures
html body div div h2: 4 Physical Structures
html body div div h2: 5 Conformance
html body div div h2: 6 Notation
html body div div h2: A References
html body div div h2: B Definitions for Character Normalization
...
< / code > < / pre >
< p > < strong > 练习 7.17： < / strong > 扩展xmlselect程序以便让元素不仅可以通过名称选择， < / p >
< pre > < code class = "language-html" > < div id=" page" class=" wide" >
< / code > < / pre >
< p > 的元素可以通过匹配id或者class， < / p >
< p > < strong > 练习 7.18： < / strong > 使用基于标记的解码API， ： ， < / p >
< p > 你可能发现下面的定义会对你有帮助。< / p >
< pre > < code class = "language-go" > import " encoding/xml"
type Node interface{} // CharData or *Element
type CharData string
type Element struct {
Type xml.Name
Attr []xml.Attr
Children []Node
}
< / code > < / pre >
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